The prior art in this general category of articles includes German Offenlegungsschriften No. 1,946,401, corresponding to U.S. Pat. No. 3,666,375, which includes a pump bracket designed as a cooling casing and having an internal hollow cylindrical portion surrounding the pump shaft and an external hollow cylindrical portion axially spaced some distance therefrom and supported on the internal portion by cooling fins. The motor casing is connected to the external portion and the pump casing is connected to the internal portion. In addition to the internal portion, the external portion accommodates the coupling situated in the region of the driving motor, a blower wheel immediately following, and a bearing. An exposed helical cooling coil is arranged between the internal and external portions as well as between two cooling fins. The spacing between the driving motor casing and the pump casing is comparatively large and the heat exchanger is acted upon only by a small portion of the air supplied by the blower wheel.